Sounds like patellar chondromalacia, but many knee injuries are similar - if your patellar tracks out of alignment, you wear away the cartilage on the underside of the knee cap. I’m no doctor just a guy who has had this diagnosis with microfissures a decade. I am still active, I avoid long distance running but still squat over 4, keeps my runs short, switched to the rower for cardio. You’ll need an mri, X-rays won’t see the cartilage damage. Check out the symptoms, might fit.